1. Field of the Invention
The present invention relates to a sealing device such as an oil seal for use in bearings such as ball bearings.
2. Description of the Prior Art
FIG. 4 shows an example of a known sealing device for a bearing which was disclosed in Japanese Utility Model Registration Publication No. 54-34090.
As shown in FIG. 4, the bearing 103 comprises an outer race 100, an inner race 101 arranged parallel to the outer race with a predetermined gap L therebetween, and a ball 102 interposed between the races 100 and 101. An oil seal 104 of the type which has metal on its radially outward periphery is forced in the gap L of the bearing 103 so as to keep the oil-filled interior of the bearing 103 sealed off from the atmosphere.
More specifically, the oil seal 104 comprises a metal ring 105 and a seal body 106 made of rubber and heat-bonded to the peripheral surface of the metal ring 105. The seal body 106 has a sealing lip portion 107 which is also made of a rubbery elastic material and formed integrally therewith. Further, the sealing lip portion 107 is provided with a first sealing lip 108 and a second sealing lip 109 branching therefrom. The first sealing lip 108 extends toward the outer side X of the bearing 103 which is exposed to the atmosphere, and the second sealing lip 109 extends toward the interior Y of the bearing 103.
The first sealing lip 108 has a sealing portion 112 formed at the intersection between a first inclined surface 110 and a second inclined surface 111, both of which face the inner race 101. The inclination of the surfaces is with respect to the rotational axis of the bearing 103. The degree of inclination of the first inclined surface 110, i.e. the angle .alpha. formed by the first inclined surface 110 and the mating surface of the inner race 101 is set at a value larger than the degree of inclination of the second inclined surface 111, i.e. the angle .beta. formed by the second inclined surface 111 and the mating surface of the inner race 101. Therefore, the above arrangement of the first sealing lip 108 of the oil seal 104 disclosed is capable of substantially preventing penetration of dust, etc. from the outer side X of the bearing which is exposed to the atmosphere, but it cannot prevent flow of oil, e.g. grease, from the interior Y of the bearing 103 which is filled with oil.
On the other hand, the second sealing lip 109 has a sealing portion 115 formed at the intersection between a first inclined surface 113 and a second inclined surface 114, both of which face the inner race 101. The inclination of the surfaces is with respect to the rotational axis of the bearing 103. The angle .alpha.' formed by the first inclined surface 113 and the mating surface of the inner race 101 is set a value smaller than the angle .beta.' formed by the second inclined surface 114 and the mating surface of the inner race 101. Therefore, the above arrangement of the second sealing lip 109 of the oil seal 104 disclosed is capable of preventing flow of oil, e.g. grease, from the interior Y of the bearing 103 which is filled with oil, but it cannot prevent penetration of dust, etc. from the outer side X of the bearing which is exposed to the atmosphere.
Problems to be Solved by the Invention
The above-mentioned prior art, therefore, suffers from the following problems: Firstly, since substantially only the first sealing lip is arranged to prevent penetration of the dust and similar foreign material from the outer side X of the bearing exposed to the atmosphere, and since the dust or similar foreign material may not be prevented from penetration solely by the first sealing lip, it is impossible to effectively prevent penetration of the dust and other foreign material from the outer side X to the interior Y of the bearing. This is because the second sealing lip is not effective to prevent penetration of the dust or similar foreign material to the interior Y of the bearing which may have entered the cavity between the first and second sealing portions.
Secondly, since the arrangement of the second sealing lip 109 is such that the second sealing lip 109 does not allow the flow of oil, e.g. grease, from the interior Y to the first sealing lip 108, the sealing lip 108 cannot be adequately lubricated, thus leading to wear and damage thereof at an early stage of usage.